Introduction

Extracorporeal membrane oxygenation (ECMO) uses cardiopulmonary bypass (CPB) technology to treat potentially reversible cardiorespiratory failure. ECMO involves drainage of venous blood, adding oxygen and removing carbon dioxide and returning the blood to the circulation. The oxygenated blood is returned to a vein in venovenous ECMO and to an artery in venoarterial ECMO.

Extracorporeal membrane oxygenation compared with cardiopulmonary bypass

ECMO differs from CPB in that it can be used for several weeks while awaiting the recovery of heart or lung function. Although superficially similar to CPB, ECMO has certain important differences that are discussed below.

Perfusion technique

The aim of CPB is to facilitate cardiac surgical procedures; it requires total venoarterial bypass (by cannulating aorta and right atrium or inferior vena cava and superior vena cava). This causes stagnation of blood in the pulmonary circulation, some chambers of the heart and some parts ofthe extra-corporeal circuit, such as the venous reservoir. To prevent clotting in these circumstances, total anticoagulation of blood is required.

In contrast with CPB, ECMO involves partial bypass, which is usually established by extrathoracic cannulation with no stagnation of blood in the pulmonary circulation or heart chambers. In addition, there is no direct exposure of blood to air as there would be intraoperatively. The ECMO circuit does not include a large reservoirorthe suction apparatus; therefore, partial heparinization provides sufficient anticoagulation. The blood flow of the pump is set at a rate that matches the metabolic needs of the patient; the haematocrit and temperature are maintained in the normal range.